This invention relates generally to radio frequency circuits and more particularly to radio frequency distributed circuits.
As is known in the art, radio frequency amplifiers configured as distributed amplifiers having a plurality of successively interconnected field effect transistors have been suggested to provide amplification of radio frequency signals. One such distributed amplifier is shown in an article entitled "2-20 GHz GaAs Travelling-Wave Power Amplifier" by Y. Ayasli et al. IEEE MTT, Vol. 32, pp. 290-294, Mar 1984. In this article is described common drain line combining techniques in which the drains from a pair of channels of successively coupled transistors are combined using a common drain line. The motivation for this technique is to increase the output power of the distributed amplifier. This is successfully accomplished by permitting the total power fed to the input circuit to be doubled, while also doubling the maximum input gate periphery for the amplifier. This provides a concomitant increase in the drain or output periphery and a corresponding reduction in the required load line output impedance bringing this value closer to the actual output impedance of the amplifier.
Electronic Support Measure Systems (ESM) are generally broadband systems, which must operate over various r.f. frequency bands to detect the presence of emitters. One type of subsystem commonly used in ESM systems is a system which measures the angle of arrival (AOA) of an emitter.
Several general techniques are used to measure angle of arrival. One technique compares or samples received signals from multiple antenna sources of the ESM system. Generally, these signals are directed to a central signal processing chain which may make various determinations on the received signals.
One technique to direct received signals is shown in FIGS. 1 and lA. A conventional broadband amplifier/switch and combiner element 10 is shown in FIG. 1 to include preamplifiers 12, SPST switches 14 and an r.f. multiplexer 16. Due to generally prevailing requirement that AOA systems cover various frequency bands, often it is required to divide the input signal into various subbands SB1-SB2, as shown in FIG. 1. Division into subbands generally require complex filtering arrangements (not shown) which increase system noise, complexity, and cost. The broadband requirement also makes the design of the r.f. multiplexer 16 complicated. With the presence of the r.f. switches 14 and multiplexer 16 in the element 10, preamplifiers 12 are needed to minimize the noise figure and to compensate for the insertion loss of the chain.
Electronic Counter Measures Systems (ECM) also are generally broadband, and have general applications for jamming a variety of emitters. Often it would be desireable to have a single path which may choose between a plurality of broadband, selectively modulated waveform signals for ultimate transmission as a jamming signal.
Accordingly, there exists the need for an improved switch/combiner element which operates over a broad range of frequencies.